Apparatus for improving the heat economy of an electrolytic cell for the production of aluminum

ABSTRACT

Method and apparatus for improving the heat economy of electrloytic cells for the production of aluminum, in which a sealed housing is provided above the bath of the cell and about the anode extending thereinto to maintain about an anode portion above the bath in said housing a volume of confined air, thereby reducing heat loss to the outer atmosphere.

United States Patent Hirt et al.

[ June 27, 1972 154] APPARATUS FOR IMPROVING THE HEAT ECONOMY OF AN ELECTROLYTIC CELL FOR THE PRODUCTION OF ALUMINUM [72] Inventors: Wilhelm Hirt, Norf; Hagen Lehnerdt,

Neuss; Ernst Weckesser, Grevenbroich/Nhn; Gottfried Weinhold, Norf; Friedrich Eilhelm Wrigge, Bad Godesberg, all of Germany 173] Assignec: Vereingte Alumlnum-Werke, Alttlengesellschait, Bonn, Germany [22] Filed: April 9, 1969 21 Appl.No.: 814,592

[30] Foreign Application Priority Data April 10, 1968 Germany ..P 17 58 149.6

[52] U.S. Cl. ..204l243 R, 204/247 51 lnt.C1 [58] Field ofSearch...

[ I References Cited UNITED STATES PATENTS 3,351,546 11/1967 Chambran et a1 ..204/245 X 2,061,146 11/1936 Ferrand ..204/247 X 2,526,876 10/1950 Sejersted ..204/247 X 3,470,075 9/1969 Johnson ..204/243 X FOREIGN PATENTS OR APPLICATIONS 37/12901 9/1962 Japan ..l04/247 193,084 5/1967 U.S.S.R. ..204/247 Primary Examiner.lohn H. Mack Assistant Examiner-D. R. Valentine Attorney-Michael S. Striker 57 ABSTRACT Method and apparatus for improving the heat economy of electrloytic cells for the production of aluminum, in which a sealed housing is provided above the bath of the cell and about the anode extending thereinto to maintain about an anode portion above the bath in said housing a volume of confined air, thereby reducing heat loss to the outer atmosphere.

8 Claims, Drawing Figure APPARATUS FOR IMPROVING THE HEAT ECONOMY OF AN ELECTROLYTIC CELL FOR THE'PRODUCTION OF ALUMINUM BACKGROUND OF THE INVENTION The present invention relates to a method and an apparatus for improving the heat economy of electrolytic cells for the production of aluminum, especially of electrolytic cells with continuous, prebaked anodes.

Electrolytic cells'for the production of aluminum differ with regard to their anodes from each other and cells with so-called green anodes or self-baking continuous anodes, as well as cells which are operated with prebaked anodes, are known in the art. Cells with prebaked anodes may be provided with discontinuously operating anodes, or as for instance disclosed in the German Pat. No. 863,999 with continuously operating anodes.

Various attempts have already been made to improve the heat economy of electrolytic cells of the aforementioned type in order to reduce the energy consumption, and it has been ascertained thata considerable reduction of the heat loss can be obtained by improving the insulation of the anode. Aluminum oxide has proven a good heat insulator for this purpose. In electrolytic cells which are operated with discontinuous anodes, which extend only for a short distance above the bath in the electrolytic cell, it is possible to properly cover the anodes with aluminum oxide to provide in this way a good heat insulation of the anodes. For such a type of electrolytic cell a decisive advantage is obtained in this way, which leads to a considerable reduction of the necessary energy for operation of the cell.

ln electrolytic cells with continuous operating prebaked anodes, as for instance disclosed in the aforementioned German patent, the individual anode blocks, which are provided with laterally extending current-conducting nipples, are superimposed from above one upon the other without necessarily changing the position of the anode block which extends in the bath. The disadvantage of this arrangement is that the portion of the anode body which projects upwardly beyond the electrolyte is considerably larger than in electrolytic cells which are operated with discontinuous anodes and that therefore a corresponding improvement of the heat economy by covering the anodes with an oxide layer is not possible. The heat radiation of anodes of this type is therefore necessarily higher as with discontinuous anodes, which in turn leads to greater heat losses and therefore a greater energy consumption. Therefore, the advantages inherent with electrolytic cells operated with continuous prebaked anodes are counterbalanced by the above-mentioned disadvantage.

It is known to provide the carbon blocks of the anodes in electrolytic cells for the production of aluminum with a protective paint or to paste aluminum foil to the outer surface thereof in order to reduce heat radiation from the outer surfaces of these blocks. Attempts have also been made to cover the carbon blocks of the anodes with heat insulating plates whereby considerable progress could be obtained, but the insulation of the end faces of the carbon blocks by mechanicalmeans is, especially in continuous operating anodes in which the carbon blocks abut with end faces thereof against each other, only very difficult to obtain.

SUMMARY OF THE INVENTION It is an object of the present invention to provide for a method and apparatus for essentially reducing the anodic heat losses and to thereby provide for an improved heat economy of electrolytic cells for the production of aluminum, especially for such cells which are operated with continuous, prebaked anodes.

It is a further object of the present invention to provide for an apparatus for the above purpose which is simple in construction so that it can be manufactured at reasonable cost and will stand up properly under extended use.

With these objects in view, the method for improving the heat economy of electrolytic cells for aluminum production, especially cells with prebaked continuous anodes extending with a considerable portion thereof upwardly from the electrolyte bath, mainly comprises the step of maintaining above the bath and about the aforementioned portion of the anode a confined volume of air to thus reduce radiation of heat from the anode to the surrounding outer atmosphere.

The apparatus of the present invention mainly comprises closed housing means covering the open end of the troughshaped container of the cell and surrounding the upper portion of the anode extending upwardly from the electrolyte in the container to maintain about the upper portion of the anode a confined volume of air to thereby reduce heat radiation from the anode to the surrounding atmosphere. In such an arrangement, the anode does not transmit the heat developed therein during operation of the cell to the outer atmosphere surrounding the cell, but the heat developed by the anode will warm up the volume of air confined in the housing until a temperature equilibrium is obtained. Thereby, the walls of the housing will be maintained at a temperature which will approach, when the walls are provided with a heat insulation, the temperature maintained in the interior of the housing. In addition, it is possible to construct the surface of the housing in such a manner that heat losses through radiation are considerably reduced. Through the combination of these two features it is possible to reduce the heat loss through the housing walls to such an extent that the heat economy of the electrolytic cell will not be negatively influenced any longer by such a heat loss. In addition, the uniform temperature maintained in the housing will be advantageous for the coking of the adhesive connecting adjacent anode blocks to each other and, due to the higher temperature maintained in the interior of the housing, the electric resistance of the anode will also be reduced.

The gases forming during the electrolytic process collect in the interior of the housing and are preferably exhausted therefrom since, due to their high fluorine content, such gases should not be discharged into the room in which the electrolytic cell is arranged. In exhausting gas from the interior of the housing care should be taken that the amount of gas discharged will not exceed the amount of gas developed during the process so that sucking of air from the outer atmosphere into the housing will be prevented. For the same purpose it is also advantageous to provide the housing with proper seals preventing air from the outer atmosphere from entering into the housing.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a schematic partially sectioned front view of the arrangement according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, it will be seen that the electrolytic cell according to the present invention comprises a trough-shaped container 2 having an upper open end and adapted to contain an electrolyte for the production of aluminum. A prebaked anode 4 extends with a lower portion thereof into the container in contact with the electrolyte therein and with a considerable portion thereof beyond the upper edge of the container 2. According to the present invention a housing 6 is provided above the open end of the container 2 and surrounding the upper portion of the anode 4 with considerable clearance to maintain above the bath in the container and about the anode4 a confined volume of air to thereby reduce heat radiation from the anode to the surrounding atmosphere.

The housing 6 includes rigid frame means comprising upper substantially horizontal guide rail means 8 and opposite additional guide rail means 10,10 which are slightly inclined with respect to a vertical inthe direction toward each other. The lower ends of the guide rail means 10 and 10' may be fixed to the floor, as shown in the drawing, or to the upper edge of the container 2. The front and rear walls 12, respectively 12' of the housing are fixedly connected to the frame means of the housing and these walls may be reinforced by reinforcing ribs 14, only one of which is shown in the drawing. The upper portion of the housing may be formed by wall means in form of a truncated pyramid l6 and the upper open end thereof is closed by a roof 18, which is movable along the horizontal guide rails 8 between a closed position, as shown in the drawing, and an open position laterally, to the left as viewed in the drawing, displaced from the closed position, so that when the roof 18 is in the open position additional anode blocks may be.

inserted into the housing on top of the anode block 4 shown therein.

The side walls 20 of the housing are movable from the closed position, shown in the drawing, in upward direction to an open position along the guide rails 10 and 10 to provide lateral access to the interior of the housing for operation of the electrolytic cell, i.e., for feeding new electrolyte into the container 2. Preferably, each of the side walls 20 comprises a pair of plates 22 and 24 which partly overlap each other. The lower plate 24 is connected by chains 26 or the like, which are guided over guide rollers 28, to motor-operated winches 30 or the like, so that the lower plate 24 may be raised by these chains. Each of the lower plates 24 has at the lower end thereof an inwardly projecting portion 32 which, during raising of plate 24, engages the bottom edge of-the upper plate 22 to raise the latter also along the respective guide rail during further upward movement of the lower plate 24. The necesary total opening to be provided will depend on the operating conditions of the electrolytic cell. It is to be understood that the side wall plates 22 and 24 are moved to the open position for a time interval as short as possible in order to reduce cooling of the interior of the housing during opening of the side walls. Proper seals are provided at theupper and lower edges of the side wall plates 22 and 24 and such seals may for instance include U-shaped members 34, 34' and 34" respectively connected to the bottom edge of the truncated portion 16 of the housing, the bottom edge of the upper plate 22 and to the ground on which the frame means are mounted and which respectively cooperate with flanges of angle irons 36, 36' and 36" respectively connected to the upper edge of the upper plate 22, the upper edge of the lower plate 24 and to the bottom edge of the latter. The spaces in the U-shaped member 34, 34 and 34" may be partly filled with aluminum oxide to provide in cooperation with the flanges of the members 36, 36' and 36" a proper seal.

The bottom edge of the roof 18 is also sealingly received in a frame 40 of U-shaped crosssection. Lateral movement of the roof 18 between the closed and then open position may be accomplished by a pair of motor-driven and reversible winches 38 and 38' connected to the roof 18 by chains 41 or the like. The chains 41 are connected to the roof 18 by means of lifting mechanisms 42, only one of which is shown in the drawing. Each of the lifting mechanisms 42 comprises a roller 44 riding on the guide rail means 8 and tumably carried by a lever 46 which is pivotally connected intermediate its ends at 48 to the roof 18, while the upper end of the lever is connected to the respective chain 41. It is evident that when the winch 38 is operated to move the cover 18 towards the left, as viewed in the drawing, the lever 46 will be tilted in counterclockwise direction about the pivot 48 to thereby lift the bottom edge of the roof out of the U-shaped member 40. A latch 50 adapted to engage with a lateral projection on the lever 46 will maintain the roof in the raised position until the latch is released again either by hand or by means not shown in the drawing.

A gas discharge opening 52 is provided in the upper truncated portion of the housing for sucking waste gas from the interior of the latter through exhaust means connected to the discharge opening 52.

A pair of U-shaped beams 54 extend transversely through an upper portion of the interior of the housing and, are connected to the latter in a manner not shown in the drawing. The U-shaped beams 54 serve to support, electrically insulated from the beams, conductor means 56 which are connected at the lower ends thereof to nipples 58 projecting laterally from the anode 4. The manner in which the conductors 56 are connected to the network is not shown in the drawing.

The roof l8 and the walls of the housing are provided at the inner surface thereof with heat insulation layers as indicated in the drawing at 18', 16, 22 and 24 and it is understood that the front and rear walls 12 and 12 of the housing are likewise provided with such an insulation. This insulation will, during operation of the cell, maintain the volume of air confined in the interior of the housing at a temperature of 180-250C, whereas in the absence of such an insulation, the temperature of the air in the housing would be maintained at a temperature of about C.

By maintaining a confined volume of air in the interior of the housing, the heat losses of the anode 4 are reduced to such an extent that at the anode side less heat is radiated to the outer atmosphere than in electrolytic cells operated with oxide covered, discontinuous anodes.

The gas exhausted through the aperture 52 may be washed according to a known process, whereby the fluorine will be recovered and in such a process the high fluorine concentration obtained with the arrangement of the present invention will be of great advantage.

it will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of methods and apparatus for improving the heat economy of electrolytic cells for aluminum production differing from the types described above.

While the invention has been illustrated and described as embodied in a method and apparatus for improving the heat economy of electrolytic cells for aluminum production and comprising prebaked continuous anodes, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In an electrolytic cell for the production of aluminum, a structure comprising a trough-shaped container having an upper open end and being adapted to contain an electrolyte; an anode extending with a portion thereof into the electrolyte and having an upper portion above the latter; and closed, heat-insulated housing means covering said open end of said container and surrounding said upper portion of said anode to maintain about the latter a confined volume of air to thereby reduce heat radiation from said anode to the surrounding at mosphere, said housing means comprising rigid frame means, a front and a rear wall fixed to said frame means, and a roof movable between a closed position closing the upper end of said housing means and an open position providing access to the interior of said housing means for insertion of anodes thereinto.

2. A structure as defined in claim 1, and including substantially horizontal guide rail means fixed to and forming part 'of said frame means for guiding said roof movable between said closed and a laterally displaced open position, and drive means connected to said housing for moving the same along said guide rail means between said positions thereof.

3. A structure as defined in claim 1, wherein said housing means comprises further a pair of opposite side wall means each including movable portions and additional opposite guide rail means forming part of said frame means for guiding said movable portions between an open and a closed position.

4. A structure as defined in claim 3, wherein said additional opposite guide rail means are inclined toward each other and wherein each of said opposite side wall means comprises a pair of vertically displaced and partly overlapping movable portions, drive means connected to the lower one of said vertically displaced portions and means connected to the lower edge of said lower portion and engaging the lower edge of the upper portion during raising of the lower portion by the drive means to thereby raise also said upper portion.

5. A structure as defined in claim 4, and including sealing means at least along upper and lower edges of said movable portions of said side wall means.

6. A structure as defined in claim 2, wherein said roof has a lower edge and including cooperating sealing means on said frame means and on said lower edge of said roof.

7. A structure as defined in claim 6, wherein said cooperating sealing means comprise a U-shaped member into which said lower edge of said roof extends,.and wherein said drive means includes lifting means for slightly lifting said roof to thereby lift said lower edge out of said U-shaped member before moving said roof laterally to its open position.

8. A structure as defined in claim 3, and including heat insulation on the walls and the roof of said housing means. 

1. In an electrolytic cell for the production of aluminum, a structure comprising a trough-shaped container having an upper open end and being adapted to contain an electrolyte; an anode extending with a portion thereof into the electrolyte and having an upper portion above the latter; and closed, heat-insulated housing means covering said open end of said container and surrounding said upper portion of said anode to maintain about the latter a confined volume of air to thereby reduce heat radiation from said anode to the surrounding atmosphere, said housing means comprising rigid frame means, a front and a rear wall fixed to said frame means, and a roof movable between a closed position closing the upper end of said housing means and an open position providing access to the interior of said housing means for insertion of anodes thereinto.
 2. A structure as defined in claim 1, and including substantially horizontal guide rail means fixed to and forming part of said frame means for guiding said roof movable between said closed and a laterally displaced open position, and drive means connected to said housing for moving the same along said guide rail means between said positions thereof.
 3. A structure as defined in claim 1, wherein said housing means comprises further a pair of opposite side wall means each including movable portions and additional opposite guide rail means forming part of said frame means for guiding said movable portions between an open and a closed position.
 4. A structure as defined in claim 3, wherein said additional opposite guide rail means are inclined toward each other and wherein each of said opposite side wall means comprises a pair of vertically displaced and partly overlapping movable portions, drive means connected to the lower one of said vertically displaced portions and means connected to the lower edge of said lower portion and engaging the lower edge of the upper portion during raising of the lower portion by the drive means to thereby raise also said upper portion.
 5. A structure as defined in claim 4, and including sealing means at least along upper and lower edges of said movable portions of said side wall means.
 6. A structure as defined in claim 2, wherein said roof has a lower edge and including cooperating sealing means on said frame means and on said lower edge of said roof.
 7. A structure as defined in claim 6, wherein said cooperating sealing means comprise a U-shaped member into which said lower edge of said roof extends, and wherein said drive means includes lifting means for slightly lifting said roof to thereby lift said lower edge out of said U-shaped member before moving said roof laterally to its open position.
 8. A structure as defined in claim 3, and including heat insulation on the walls and the roof of said housing means. 